DESCRIPTION: (Applicant's Description) Evidence is building to support physical activity as a modifiable lifestyle factor in cancer prevention, both directly and indirectly through obesity prevention. However, as stated in the NIH/NCI PA-99-163, "only a small proportion of the U.S. population participates in regular physical activity. Robust methods must be developed to examine and explain the determinants of changes in these behaviors." Rates of sedentary behavior are rising in adults and children, as are rates of obesity. Physical inactivity will likely continue to increase over time without the development of successful physical activity interventions. However, successful interventions against sedentary behavior cannot be developed without a better understanding of the determinants of physical activity behaviors. Our research and that of others among adults has shown that how we perceive ourselves athletically and how others perceive us are plausible determinants of whether we are physically active. In this application, in an ethnically diverse sample, we propose to construct and validate a psychometric scale that measures parental beliefs about their 4th and 5th grade children and physical activity as determinants of children's athletic identity and participation in physical activity. Identity formation begins in childhood and is strongly influenced by parents, who can encourage or discourage developing athletic identities. Since people are resistant to change of ingrained identities that are firmly supported by social structure, parental influence on a child's athletic identity could have far reaching implications on how much physical activity they do. Understanding how parents influence children's physical activity and the ethnic/cultural differences which likely exist will provide a new mechanism for change in future interventions to increase regular physical activity and thereby reduce the risk of several activity-related cancers. Long-term physical activity patterns that are sustained over many years likely reflect a core aspect of the self: a relevant self-definition as a physically active person that is initiated in childhood. Our project represents an innovative approach to understanding and increasing regular physical activity in the primary prevention of cancer.